1. Field of the Invention
The present invention relates to the replacement of pre-placed prosthetic joints and more particularly to a method and apparatus for removing the cement mantle used to secure the pre-placed joint in place. In its more particular aspects, the invention is concerned with such a method and apparatus for removing the cement mantle to secure the ball of a prosthetic hip joint to the patient's femur.
Prosthetic hip and knee joints have become relatively commonplace. Unfortunately, however, there has also been a progressive rise in the incidence of the nonseptic failure of such joints which necessitates revision surgery to affect their replacement. The leading cause of the nonseptic failure of hip joints is the loosening of the femoral side of the prosthetic appliance. This is generally the result of loosening of the cement securing mantle for the appliance from the cavity in the femur within which the mantle is received.
Revision surgery for the replacement of a failed joint requires that both the prosthetic appliance and the mantle holding it in place within the bone cavity be removed. The old prosthetic device is usually easily removed using a slap-hammer, since its surface is smooth and separable from the underlying cement mantle. The cement mantle, however, is tightly adherent to the surrounding bone and generally remains so adhered, even after the prosthetic device is removed.
2. Description of the Relevant Art
Removal of the adhered cement mantle is presently performed by progressively chipping the mantle away using a hammer and chisel. This method is tedious and the possibility of the chisel going past the mantle and fracturing the underlying bone is present. Other methods of removing the cement mantle, using powered drilling and boring devices, are similarly tedious and dangerous to the bone.
Prior revision surgery for the replacement of prosthetic hip joints also often includes a trochanteric osteotomy to remove the greater trochanter. Although this exposes the cement mantle and makes it easier to work upon, it generally does not eliminate the necessity for chipping the mantle away with a hammer and chisel to affect its removal.
Methylmethacrylate cement is the most accepted type of cement used to secure prosthetic joint appliances to bone. This cement is supplied to the surgeon packaged in two sterile components. One component is a liquid methyl methacrylate monomer and the other is a finely divided powder mixture of polymethyl methacrylate, methyl methacrylate-styrene-copolymer. At the time of use, the powder and liquid are mixed, resulting in the exothermic polymeric formation of a soft pliable dough-like mass. As the reaction progresses, within a few minutes a hard cement-like complex is formed. It is this complex which forms the cement mantle which the present invention is designed to remove.
Old hardened methylmethacrylate cement is capable of being partially dissolved and softened by the application of new like fluid cement thereto. The resulting composite of old and new cement cures into an integral bonded composite, generally within about ten minutes. Although the present invention relies upon this characteristic of methylmethacrylate cement, it may find equal application to other cements, so long as an adequate bond is provided between the old and new cement.
In the method of the invention described in the parent application, Ser. No. 255,650, a mass of new fluid methylmethacrylate cement is placed in contact with the hardened mantle of old methylmethacrylate cement desired to be removed. A pulling appliance is then imbedded within the fluid cement and the mass of cement is permitted to cure and harden, thus forming a bond between the appliance and the mantle of old cement. Tension is then applied to the pulling mantle to pull the appliance and the entire bonded mantle from the bone.
While this method is an improvement over the other prior art, it still suffers from a significant problem. In some patients, particularly those of advanced age, the bones may become brittle, and the application of sufficient force to dislodge the entire hardened mantle of cement may shatter part of the surrounding femur.